1. Field of the Invention
The present invention relates to a device for controlling the recording power of an optical beam used to record information onto an optical recording medium and more particularly to a device for controlling the recording power in digital video disc (DVD) drives.
2. Description of the Related Art
Various optical recording media are known. One example is a write once read many (WORM) optical disk to which information can be written once using an organic dye material. Another example is a rewritable optical disk that can be rewritten repeatedly using a phase-changing material or a magneto-optical material. With these optical recording media, information is recorded by making use of the fact that a physical property of the recording surface is varied by thermal energy of an optical beam impinging on the recording surface.
In the case of these optical recording media, the recording power may not be optimal, depending on the recording medium, even if the same recording material is used in every commercial product, and if uniform optical beam power is established for the same material, because the characteristics of the material are different among the individual commercial products.
In this kind of information storage system for recording information on such an optical recording medium, optimum power control (OPC) is provided before information is started to be recorded. That is, the recording power of the optical beam is optimized for the optical recording medium.
The optimum power control (OPC) is provided in the manner described below. Usually, before recording is started, trial writing is done into a region formed in a given position of the recording medium, called a PCA (power calibration area), while varying the power value within a given range. The tentatively written testing information is reproduced. The power value producing a reproduced signal having the least jitter is established as the recording power best suited for the recording medium. In this way, the power can be optimized under these conditions.
Generally, the recording conditions vary slightly depending on the recording position even if the same optical recording medium is used. For example, fingerprints might be scattered on the recording surface of the optical recording medium or the medium may be warped, varying the shape. This makes the recording conditions at each recording position different from the recording conditions in the power calibration area (PCA) described above. Accordingly, if recording is made over the whole surface of the recording medium with the given optimum power found in the PCA, the recording power might be excessive or insufficient depending on the recording position.